The invention relates generally to meltblowing processes and to die assemblies for practicing meltblowing processes, and more particularly to die assemblies with a plurality of adhesive dispensing orifices flanked on each side by air dispensing orifices, wherein adhesive flows from the plurality of adhesive dispensing orifices are drawn and attenuated by relatively high velocity, high temperature air flows from the air dispensing orifices to form adhesive filaments.
Meltblowing is a process of forming fibers or filaments by drawing and attenuating a first fluid flow, like molten thermoplastic, with shear forces from an adjacent second fluid flow, like heated air, at high velocity relative to the first fluid flow. These meltblown filaments may be continuous or discontinuous, and range in size between several tenths of a micron and several hundreds of microns depending on the meltblown material and requirements of a particular application. The applications for meltblowing processes include, among others, the formation of non-woven fabrics and the dispensing of meltblown adhesive materials for bonding substrates in the production of a variety of bodily fluid absorbing hygienic articles like disposable diapers and incontinence pads, sanitary napkins, patient underlays, and surgical dressings.
In U.S. Pat. No. 5,145,689 entitled "Meltblowing Die" issued on Sep. 8, 1992 to Allen et al., for example, an elongated die assembly includes a triangular die tip defined by converging surfaces that form an apex with a plurality of orifices arranged in a series therealong. A continuous air passage formed by air plates disposed along and spaced apart from the converging surfaces of the die tip directs converging sheets of high temperature, high velocity air along the converging surfaces of the die tip toward the apex where the high velocity air draws and attenuates polymer flows dispensed from the plurality of orifices. The U.S. Pat. No. 5,145,689 also discloses an actuatable valve assembly located upstream of the plurality of orifices to selectively control the polymer flow to the orifices in the die tip.
The inventors of the present invention recognize that compressing and heating air required for forming meltblown adhesives and other filaments is an expensive aspect of the meltblowing process. The inventors recognize also that drawing and attenuating fluid dispensed from a series of orifices in a die with converging air flow sheets disposed along opposing sides of the series of orifices is an inefficient configuration for meltblowing processes that require substantial amounts of compressed air, which is costly. More specifically, a substantial portion of each air sheet contributes very little to the meltblowing process since only those portions of the air sheet proximate the opposing flanking sides of the individual fluid flows has any significant affect on the drawing and attenuation of the dispensed fluid. Also, only the shear component of the converging air flow sheets, which is parallel to the dispensed fluid flow direction, contributes to the drawing and attenuation of the dispensed fluid.
The compressive component of the converging air flow sheets, which flows perpendicular to the dispensed fluid flow direction, does not contribute to the drawing and attenuation of the dispensed fluid. The inventors recognize further that maximizing the shear component of the air flow will maximize the rate at which the meltblown material is drawn and attenuated and reduce the required amounts of compressed air, which results in reduced production costs.
The inventors of the present invention recognize that any residual fluid along a fluid supply conduit between an actuatable fluid supply control valve and a fluid dispensing orifice has a tendency to continue to flow from the fluid dispensing orifice after the fluid supply has been terminated. In applications that require accurate dispensing of a meltblown fluid including the application of meltblown adhesives onto substrates, however, any continued fluid flow from the fluid orifice after the fluid supply is terminated is highly undesirable. The inventors recognize also that it is necessary in many meltblown adhesive applications, including the manufacture of bodily fluid absorbing hygienic articles, to uniformly produce and apply the meltblown filaments. More specifically, it is necessary to apply a consistent layer of meltblown material onto a substrate or other surface and to produce a well defined interface or boundary between areas covered and areas not covered by the meltblown material. In the production of bodily fluid absorbing hygienic articles, for example, accurate control over the application of meltblown adhesives onto specific areas of a substrate is absolutely necessary since only designated portions of the substrate require bonding whereas other areas either do not require bonding or are discarded as waste.
The inventors of the present invention recognize further that prior art manufacture and fabrication of meltblowing dies limits the scope meltblowing applications for which the dies may be used. More specifically, many meltblowing dies require precision machining techniques to fabricate the often very small diameter fluid dispensing orifices and other features of the die. For some applications the die fabrication requirements are at the limits of existing technologies, and in many other applications the die fabrication requirements are cost prohibitive.
In view of the discussion above among other considerations, there exists a demonstrated need for an advancement in the art of meltblown processes and apparatuses for practicing meltblowing processes.
It is therefore an object of the invention to provide novel meltblowing methods and novel apparatuses for practicing meltblowing methods that overcome problems in the prior art.
It is also an object of the invention to provide novel meltblowing methods and apparatuses that are economical and useable for applying meltblown adhesives onto substrates in the production of bodily fluid absorbing hygienic articles.
It is another object of the invention to provide novel meltblowing methods and apparatuses that reduce amounts of fluid required for forming meltblown filaments, and in particular for reducing amounts of air required for drawing and attenuating meltblown adhesive filaments.
It is another object of the invention to provide novel meltblowing methods and apparatuses for eliminating residual fluid flow from fluid dispensing orifices of a body member after terminating fluid supplied to the orifices.
It is another object of the invention to provide novel meltblowing methods and apparatuses for controlling application of meltblown filaments, and more particularly for selectively controlling dispensed fluid mass flow rates, and for selectively controlling dispensed fluid vacillation parameters, and for selectively controlling patterns of meltblown filaments applied onto a substrate including edge definition of the meltblown filaments.
It is yet another object of the invention to provide a novel meltblowing die assembly comprising a plurality of laminated members for distributing first and second fluids to corresponding first and second orifices arranged in an alternating series, wherein each of the first orifices is flanked on both substantially opposing sides by one of the second orifices, and wherein the first and second fluid flows are directed substantially non-convergently.
It is still another object of the invention to provide a novel meltblowing die assembly comprising a plurality of laminated members or plates for distributing first and second fluids to corresponding first and second orifices arranged in an alternating series of first and second orifices, wherein each first orifice and a second orifice disposed on both substantially opposing sides of the first orifice form an array of fluid dispensing orifices, and wherein a plurality of at least two arrays are arranged either collinear, or parallel, or non-parallel to each other in the meltblowing die assembly.
It is another object of the invention to provide a novel meltblowing die assembly mountable on a die adapter assembly which supplies fluids to the die assembly, wherein a plurality of at least two die adapter assemblies are arranged adjacently to form an array of adjacent die assemblies.
These and other objects, features and advantages of the present invention will become more fully apparent upon consideration of the following Detailed Description of the Invention with the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced by corresponding numerals and indicators.